1. Field of the Invention
The present invention relates to an impermeable laminate membrane bag having an extremely low permeability, and more particularly, to a laminate membrane bag which is suitable for implantation into living organisms.
2. Brief Description of the Prior Art
Silicones and fluoropolymers were established as medical plastics because of their outstanding compatibility with tissue and stability in living organisms. In particular, silicones are used for extracorporeal circulation circuits, implanted shunt for hemodialysis, catheters, mamma prosthesis, etc., and fluoropolymers are used for trachea cannula, etc. In addition, silicones are used for gas permeation membranes of pump-oxygenators and soft contact lenses, by virtue of their outstanding compatibility with living organisms, stability, and gas permeability.
Flexible and elastic silicone rubber membranes are formed into a baggy implantation material, which is used to fill the voids in the living organisms after such membranes have been filled with silicone gel or physiological saline. Examples of such a use include mamma prosthesis and testis prosthesis. The baggy implantation material which contains a gel or liquid suffers from the disadvantage that its contents, e.g., the silicone gel, may permeate through the membrane into the living organism, causing the connective tissue surrounding the prosthesis to become tylotic, and then shrink. This tissue area has a hard feel, when touched from outside. Therefore, to avoid this undesirable result it is necessary to prevent the silicone filler from leaking through the membrane. If the contents leak through the membrane, the baggy implantation material shrinks in size, losing its initial shape. Thus, if a silicone membrane is to be used for such an implantation material, the permeability of the silicone membrane should be kept low. For instance, in the case of mamma prosthesis, the permeation is reduced by gelling or polymerizing the silicone oil in the silicone rubber membrane bag so as to decrease permeable low-molecular weight silicone. Nevertheless, the residual low-molecular weight silicone permeates over a prolong period of time, leading to the previously discussed problem. An attempt has been made to replace silicone with physiological saline, but water also permeates the membrane and does not permit shape retention. Thus, it has not been possible to prevent the permeation by polymerizing the content of the bag.